This invention relates to a liquid monomeric composition which has anaerobic curing characteristics, that is, a composition which undergoes spontaneous polymerization to a solid state in the absence of air or substantial amounts of oxygen.
Sealant compositions of this general type have been formulated for bonding closely facing metal surfaces such as threaded joints, for joining nuts to bolts without lock washers, gears to shafts for rotation therewith, and the like. Such compositions are precatalyzed or pre-reacted monomeric compositions which polymerize in the absence of oxygen but the curing of which is inhibited by oxygen. While such compositions are stored in partially empty containers or air-permeable plastic containers, sufficient amounts of oxygen continuously contact the anaerobic composition to maintain the composition in an uncured, liquid state. However, when an anaerobic composition of this general type is placed between surfaces to be bonded or sealed and atmospheric oxygen, i.e., air, is effectively excluded, polymerization or cure of the composition commences within a relatively short time period and the composition will set to a solid state. The polymerization in the absence of air is accelerated by contact with active metals.
Anaerobic compositions generally are composed of polymerizable acrylic ester monomers and peroxide, hydroperoxide, and other similar polymerization initiators therefor together with amine, amide or imide latent polymerization accelerators which do not initiate polymerization but only accelerate the polymerization reaction once it has begun. In order to prevent premature polymerization of the monomer, it has been common practice to incorporate within the anaerobic compositions a small amount of a quinone-type stabilizer which inhibits free radical polymerization. Illustrative prior art anaerobic compositions are disclosed in U.S. Pat. Nos. 2,895,950; 3,041,322; 3,043,820; 3,046,262; 3,203,941; 3,218,305; 3,300,547; 3,720,656; 3,957,561; 3,980,627 and others.
Some of the anaerobic compositions heretofore known cannot be used on passivated metal surfaces such as stainless steel, cadmium-coated steel, zinc-coated steel, and the like, without the prior application of a primer while other such compositions, which are suitable for use with such surfaces, tend to promote corrosion when used on ordinary steel surfaces. The composition of the present invention, on the other hand, can be used with stainless steel and other passive metal surfaces as well as with ordinary steel to provide a relatively high-strength bond and without promoting corrosion. Additionally, the present composition exhibits relatively low toxicity as compared to other commercially-available anaerobic sealant compositions.